For three decades, primatologist Roger Fouts has been involved in language studies of the chimpanzee, the animal most closely related to human beings. Among his subjects was the renowned Washoe, who was "endowed with a powerful need to learn and communicate," and who developed an extraordinary vocabulary in American Sign Language. Another chimpanzee, Fouts writes, "never made a grammatical error," which turned a whole school of linguistic theory upside down. While reporting these successes, Fouts also notes that chimpanzees are regularly abused in laboratory settings and that in the wild their number has fallen from 5,000,000 to fewer than 175,000 in the last century.